For the purpose of identifying the acoustic characteristics of honeycomb sandwich panels, finite element method (FEM), combined with boundary element method (BEM), has been widely used. However, the latter approach is not always applicable to high frequency analyses since it requires a large number of FEM/BEM meshes. In order to reduce computational resources and modeling times, a hybrid analytical/finite element method (HAFEM) is described that uses a finite element approximation in the thickness direction, while analytical solutions are assumed in the plane directions. Thus, it makes it possible to use a small number of finite elements, even for high frequency analyses. By using the HAFEM, the wave transmission, propagation, and radiation characteristics of the honeycomb sandwich panels are investigated. The proposed HAFEM procedure is validated by comparing the predicted transmission loss (TL) results to the measured ones. Through the use of the HAFEM model of a honeycomb sandwich panel, it is shown that the structural responses of the panel converge asymptotically to flexural waves in the low audible frequency region, core shear waves in the high audible to ultrasonic frequency region, and skin flexural waves in the high ultrasonic frequency region. Coincident frequencies occur at the transition region from the flexural to core shear wave behaviors. From the TL sensitivities of various panel design parameters, the most dominant design parameters contributing to the TL results are determined as a function of frequency. In order to improve the acoustic performance of the honeycomb sandwich panel while satisfying weight and strength requirements, a new double core honeycomb sandwich panel is designed to have the same mass per unit area as the baseline single core panel but have a larger equivalent flexural stiffness than that of the baseline panel.